I have the kessil fixture. I'm going to warn you, low tech is hard with this tank. I say that because I tried the same thing. I tried doing low tech with my 25g cube - here's how it started out: http://fusiongt.com/image/aquarium/DSC_2940-small.jpg
Unfortunately it ended up getting lots of bba and before I knew it, it was out of control. I even had the light 14-15 inches above the tank (which is already pretty tall at 18 inches) when Kessil says to put it just a foot above. I had the lights on 8 hours a day (so not super long like 10-12). I put even more plants than in the picture with more ferns and anubias along with floating frogbite. The plants grew really well but after 2 months it just was more light than my plants needed and ultimately led to bba algae; now I'm injecting c02, adding lots of stem plants, and spot dosing excel to get rid of it.
So even though low tech sounds tempting, when you add that monster of a light to it, it suddenly becomes difficult. You saved money on the tank with it being on sale, so I say just invest in a c02 setup. Inline diffuser with your canister filter will make it look really clean and you can grow whatever plants you want in there at a good rate. Low tech only works if your light setup isn't phenomenal which the Kessil light is. Just splurge a little because this thing will look gorgeous but not if its over run by algae due to the light being way stronger than you think it'll be.
And really, the only reason I didn't go with c02 to begin with was because I didn't want to trim the plants that often... but now after getting bba for the first time, I realize that having to trim your plants to often because they're growing like crazy is a GREAT problem to have. I love the dimensions of your tank and know it'll turn out fantastic - if you decide to go low tech, just take my warning and limit the amount of time you keep the light on.
I'm sure low tech can be done with the Kessil light, but now that I've experienced it, I've come to the conclusion as to simply: why? Why get an amazing light and then try to stop it from doing its job. Why get a Ferrari and drive it super slow? Let this rockstar light fixture shine and grow the heck out of your plants... which will require c02.
I also just looked at your sig and other tanks - you know what you're doing... you know how well c02 helps tanks so don't fight it! Just splurge man. Make this tank as good as you know how because it's obvious you know what you're doing. You'll get bored of low tech when the plants just don't grow as well as you're used to.
edit - Finally, if you get the gooseneck fixture for Kessil, I don't know how that'll do with your very wide tank as with any light, especially LEDs, it gets weaker as you get further from the light source. The Kessil beams down its light super strong so you would need to keep it fairly high above the tank (perhaps higher than the gooseneck allows though I'm not sure) and with your dimensions may need it to be further out to be closer to the middle. I'd also watch out for glare from your TV assuming that your couches are pointed to a flatscreen. Not a huge deal but if you have a plasma it could reflect pretty bright - but then again, you may watch it more at night when the tank's light has gone off.